Abstract

In spite of many progresses achieved both with theories and with experiments in studying light propagation through diffusive media, a reliable method for accurate measurements of the optical properties of diffusive media at NIR wavelengths is, in our opinion, still missing. It is therefore difficult to create a diffusive medium with well known optical properties to be used as a reference. In this paper we describe a method to calibrate the reduced scattering coefficient, μ́s, of a liquid diffusive medium and the absorption coefficient, μa, of an absorbing medium with a standard error smaller than 2% both on μ́s and on μa. The method is based on multidistance measurements of fluence into an infinite medium illuminated by a CW source. The optical properties are retrieved with simple inversion procedures (linear fits) exploiting the knowledge of the absorption coefficient of the liquid into which the diffuser and the absorber are dispersed. In this study Intralipid diluted in water has been used as diffusive medium and Indian ink as absorber. For a full characterization of these media measurements of collimated transmittance have also been carried out, from which the asymmetry factor of the scattering function of Intralipid and the single scattering albedo of Indian ink have been determined.

Figures (4)

Measurements of μeff : The figure reports ln[rΦ(r)] as a function of the source receiver distance r for three values of Intralipid concentration. Marks: experimental results; continuous lines: linear fits of the results.

Calibration of Intralipid: The figure reports μ2eff (ρil)/ρil as a function of volume concentration ρil. The coefficients εail and έ
sil are obtained from the slope and the intercept of the straight line that best fits the results.